1. Field of the Invention
This invention relates to a damping adjustable shock absorber for a bicycle riding on different road conditions.
2. Description of the Related Art
Shock absorbers for bicycles are used to provide a damping effect to mitigate shocks that are generated upon riding on a rough road. However, conventional shock absorbers normally provide a limited range of damping effects and cannot be adjusted to provide a wider range of damping effects for different road conditions.
Therefore, it is an object of the present invention is to provide a damping adjustable shock absorber for a bicycle that is capable of overcoming the aforementioned drawback.
According to the present invention, a shock absorber comprises: opposing first and second cylinders which are coupled to and which are movable toward each other in an axial direction relative to the first and second cylinders during a compression stroke and away from each other during an extension stroke, the first cylinder having opposing first fixed end and first free end, the second cylinder having opposing second fixed end and second free end, the second free end extending through the first free end and into the first cylinder in the axial direction; a hollow shaft disposed in and extending through the first cylinder and into the second cylinder in the axial direction, and having a secured end that is fixed to the first fixed end of the first cylinder, and an end section that is opposite to the secured end, that is disposed in the second cylinder, that defines an inner space, and that is formed with a opening; a first piston disposed in the first cylinder, sleeved movably on the hollow shaft so as to cooperate with the first cylinder to confine a first chamber therebetween, and coupled securely to the second free end of the second cylinder so as to be moved by the second cylinder in the axial direction, the first chamber being filled with an inner gas; a second piston disposed in the second cylinder and sleeved securely on the end section of the hollow shaft so as to cooperate with the first piston and the second cylinder to confine second and third chambers thereamong at two opposite sides of the second piston, and so as to be moved by the hollow shaft in the axial direction, the second and third chambers being filled with a damper-fluid, the second piston being formed with first and second down-flow channels and a up-flow channel, the second down-flow channel being constantly in fluid communication with the opening, which is capable of being in fluid communication with the third chamber via the inner space when exposed to the inner space; a first valve associated with the first down-flow channel for permitting unrestricted low velocity flow of the damper-fluid from the third chamber to the second chamber via the first down-flow channel during the compression stroke, in which, the first and second cylinders move toward each other in the axial direction, which, in turn, moves the hollow shaft and the second piston toward the second cylinder to compress the damper-fluid in the third chamber, and moves the first piston toward the first cylinder to compress the inner gas in the first chamber; a second valve associated with the second down-flow channel for permitting a medium velocity flow of the damper-fluid from the third chamber to the second chamber via the second down-flow channel and the opening during the compression stroke; a third valve associated with the up-flow channel for permitting unrestricted low velocity flow of the damper-fluid from the second chamber to the third chamber via the up-flow channel during the extension stroke, in which, the compressed damper-fluid in the third chamber pushes the hollow shaft and the second piston to thereby move the first cylinder away from the second cylinder, and the compressed inner gas in the first chamber pushes the first piston to thereby move the second cylinder away from the first cylinder; and a damping adjusting rod disposed fittingly in the hollow shaft, and movable in the axial direction to a first axial position, in which, the opening is blocked by the damping adjusting rod and is not exposed to the inner space so that the medium velocity flow of the damper-fluid from the third chamber to the second chamber via the opening and the second down-flow channel is not permitted, and to a second axial position, in which, the damping adjusting rod moves away from the opening so as to permit the opening to be exposed to the inner space and so as to permit the medium velocity flow of the damper-fluid from the third chamber to the second chamber.